A plasma apparatus is widely used in manufacturing a semiconductor device, a flat panel display and the like to perform a processing such as oxide film formation, crystal growth of a semiconductor layer, etching and ashing.
Among such plasma apparatuses, there is a radio frequency plasma apparatus which introduces a radio-frequency wave into a processing chamber from an antenna and generates high density plasma. The radio frequency plasma apparatus is characterized in that it can generate plasma stably even when the pressure of plasma gas is relatively low, and thus, can be applied widely.
FIG. 8 is a cross sectional view showing a configuration of an etching apparatus which uses a conventional radio frequency plasma apparatus. In the etching apparatus, a cylindrical processing chamber 511 opened at an upper portion and a dielectric plate 512 covering the upper opening of processing chamber 511 form a hermetic chamber.
At a bottom of processing chamber 511, an exhaust port 515 is provided for vacuum evacuation. At a sidewall of processing chamber 511, an etching gas supply nozzle 517 is provided. Processing chamber 511 accommodates a mounting table 522 for placing thereon a substrate 521 to be etched. Mounting table 522 is connected to a radio frequency power supply 526 for bias voltage.
Above dielectric plate 512, a dipole antenna 530 is arranged to supply a radio-frequency wave into processing chamber 511 through dielectric plate 512. Peripheries of dielectric plate 512 and antenna 530 are covered with a shield member 518. Dipole antenna 530 is connected to a radio frequency power supply 543 for power supply.
FIG. 9A, showing a configuration of dipole antenna 530 shown in FIG. 8, is a plan view of dipole antenna 530 taken from a line IX-IX in FIG. 8. FIG. 9B shows a coordinate system thereof.
Dipole antenna 530 has two conductor rods 531 and 532 arranged linearly in parallel with the main surface of dielectric plate 512. When the wavelength of the electromagnetic field above dipole antenna 530 is λg, the length of each of conductor rods 531 and 532 is about λg/4, and the entire length L of antenna 530 is about λg/2. Radio frequency power supply 543 for power supply is connected to opposite end portions of conductor rods 531 and 532, which are spaced apart.
For convenience of description, a rectangular coordinate system is established as follows: the center axis of conductor rods 531 and 532 is defined as the x-axis, and the center between opposite end portions of conductor rods 531 and 532 is defined as the origin ∘. An axis orthogonal to the x-axis and parallel with the main surface of dielectric plate 512 is defined as the y-axis. An axis orthogonal to the main surface of dielectric plate 512 is defined as the z-axis.
An operation of the etching apparatus shown in FIG. 8 will now be described. Processing chamber 511 is evacuated to a prescribed degree of vacuum, with substrate 521 placed on the top surface of mounting table 522. An etching gas is then supplied through nozzle 517 with its flow rate being controlled. In this state, when power is fed from radio frequency power supply 545 to dipole antenna 530, resonance occurs because the entire length L of antenna 530 is about λg/2. Consequently, large current flows through antenna 530, from which a radio-frequency wave is emitted. The radio-frequency wave passes through dielectric plate 512 to be introduced into the processing chamber.
The electric field of the radio-frequency wave introduced into processing chamber 511 causes ionization of the gas in processing chamber 511 to generate plasma at the space 550 upper of substrate 521 that is the object of processing. The plasma diffuses in processing chamber 511 and has its energy and anisotropy controlled by a bias voltage (several hundred kHz-several MHz) applied to mounting table 522 for use in the etching process.
FIG. 10A and FIG. 10B are schematic views showing the radiation characteristic of dipole antenna 530 shown in FIG. 9A. FIG. 10A and FIG. 10B show electric field intensity distribution in the xz-plane and in the yz-plane, respectively.
Intensity of the electric field formed by dipole antenna 530 is at maximum at origin ∘, i.e., the center of dipole antenna 530, and is gradually lowered in proportion with a distance from origin ∘ in the direction of the x-axis or the y-axis. It is noted that since the radio-frequency wave output from dipole antenna 530 is a linearly polarized wave parallel with the x-axis, the electric field intensity distribution in the yz-plane exhibits a gentle gradient whereas that in the xz-plane exhibits a steep gradient.
When an electric field with the intensity distribution as shown in FIG. 10A and FIG. 10B is used to generate plasma, plasma density is lowered at the outer periphery (the peripheral edge at a plane parallel with the xy-plane) of upper space 550 of substrate 521.
Furthermore, plasma generated in space 550 diffuses toward mounting table 522. Plasma traveling from the outer periphery of space 550 to the sidewall of processing chamber 511 dissipates. Thus, even though the plasma density in upper space 550 is kept uniform, the plasma arriving in the neighborhood of the periphery of the top surface of substrate 521 is smaller than that arriving around the center of substrate 521. Consequently, the plasma density in the neighborhood of the periphery of the top surface of substrate 521 is lower than that around the center thereof.
With these two synergistic effects, when dipole antenna 530 is used to generate plasma, the plasma processing rate is disadvantageously lowered in the vicinity of the periphery of substrate 521 where plasma density is low.